PX400 Wein Cell Mercury Replacement Battery for Pentax Spotmatic cameras
Wein Cell mercury replacement battery PX400, also known as MRB400, RM400R and V400PX.
The original 1.35V mercury batteries are no longer produced and silver oxide or alkaline batteries provide too high a voltage (1.55V). The Wein Cell mercury replacement battery PX-400 produces 1.35V and can be used to replace the original battery in many Pentax and Beaulieu cameras including the following:
Diameter: 11.2mm (9.6mm without black collar), height: 3.6mm.
Also known as: RM400, PX400, EPX400, RM400, H-B, V400PX
To use this battery, the tab on the back of the battery must be removed. This allows air to enter the cell and start the chemical reaction in the battery. After about 30 minutes, the battery is fully activated and ready for use. The Weincell PX-400 battery uses a proprietary electrolyte and smaller number of air holes to ensure a longer battery life.